Attack and decay switching circuit for electronic musical instrument

ABSTRACT

A switching circuit to be used in an electronic musical instrument for changing the time-constant characteristics of an envelope of the musical tone signal is composed of a gate, an envelope-forming capacitor, a key switch connected in parallel to said capacitor, at least one of series circuit each consisting of a capacitor and a current-limiting element, and a time-constant changing switch, said at least one of series-connected circuits being further connected in parallel with said envelope-forming capacitor, and said time-constant changing switch being so arranged that said current-limiting element is thereby shortcircuited or not short-circuited.

United States Patent [72] Inventor Toshiro Matsuura Iwata-shi, Japan [21] Appl. No. 812,815 [22] Filed Apr. 2, 1969 [45] Patented Jan. 19, 1971 [73] Assignee Nippon Gakki Seizo Kabushiki Kaisha Nakazawa-Cho, I-Iamamatsu-Shi, Shizuoka-ken, Japan [54] ATTACK AND DECAY SWITCHING CIRCUIT FOR ELECTRONIC MUSICAL INSTRUMENT 4 Claims, 7 Drawing Figs.

[52] U.S. C1 84/].26 [51] Int. Cl G10h 1/02 [50] Field ofSearch 84/1.13, 1.24, 1.26

[5 6] References Cited UNITED STATES PATENTS 3,109,878 11/1963 Hanert 84/1.12

3,150,228 9/1964 Gibbs et al 84/126 3,180,919 4/1965 Stiefel 84/ l .26 3,383,453 5/1968 Sharp 84/126 Primary Examiner-W. E. Ray Attorney-Holman, Glascock, Downing & Seebold ABSTRACT: A switching circuit to be used in an electronic musical instrument for changing the time-constant characteristics of an envelope of the musical tone signal is composed of a gate, an envelope-forming capacitor, a key switch connected in parallel to said capacitor, at least one of series circuit each consisting of a capacitor and a current-limiting element, and a time-constant changing switch, said at least one of series-connected circuits being further connected in parallel with said envelope-forming capacitor, and said time-constant changing switch being so arranged that said current-limiting element is thereby short-circuited or not short-circuited.

OUTPUT 2 -EzlVl PATENTEUJANISISYI 3557297 sumaorz- I INPUT F' 4 FIG. 6

, I (v) El I I 0, I 2 1D Q-EZ'W) R o K. o I FIG. 5 POTENTIAL -E| 7'=.c|R| 3 2 POINT b POTENTIAL (V) INVENTOR 7 :11 im: Mons-a04 Mn-w AM J D BY I I W ATTORNEYS ATTACK AND DECAY SWITCHING CIRCUIT FOR ELECTRONIC MUSICAL INSTRUMENT BACKGROUND OF THE INVENTION This invention relates generally to the field of electronic musical instruments, and more particularly to improvements in switching circuits to be used therein for changing at will the attack and decay or the rising or attenuation characteristics of the envelope of musical tones.

A representative example of switching circuits used heretofore is illustrated in FIG. 1 of the accompanying drawings (described hereinafter). In this circuit under normal conditions, the point a of a capacitor C is charged to a potential of E, through a resister R and transistor TR is broughfto an interrupting condition. When a key switch K is closed, the charge in the capacitor C is discharged through a resistor R,, thereby lowering the potential at a to E,, and the transistor TR is brought into the conductive state. This condition is brought back to the original state when the switch K is opened again. In such cases, the rising time and the attenuation time of the envelope ofa musical tone are substantially defined by the time constants CR, and CR respectively.

In order to provide the instrument for the long sustain time, the capacitor C in the above described circuit should be of a considerably large capacitance. But with this large capacitance, the resistance values of R, and R should be extremely low if it is desired to shorten the rising time (also the attenuation time). This, in turn, causes a large discharge current at the time the switch K is closed and also unnecessary large currents flow through the resistors R,, R,. In addition, because the time constants for the rising time and the attenuation time restrict each other, there was difficulty in determining each of the time constants at will independently.

SUMMARY OF THE INVENTION Therefore, the primary object of the present invention is to provide an improved switching circuit to be used in an electronic musical instrument, wherein the above described drawbacks are substantially overcome.

Another object of this invention is to provide an improved construction of a switching circuit, whereby the time constants during rising time and attenuation time of an envelope of a tone signal can be changed at will with the operation of a switch.

Still another object of the invention is to provide an improved switching circuit, whereby the change of the above described time constants is attainable in a simple manner and with an economized construction of the switching circuit.

A further object of the invention is to provide a novel construction of the switching circuit, whereby the above described time constants can be changed in a multitude of different values.

The above described and further objects of the invention are accomplished by an improved and partly novel construction of the switching circuit comprising: an envelope-forming capacitor of a smaller capacitance, at least one of series-con nected circuits each consisting of a capacitor of a larger capacitance and a current-limiting element, and a time constant change switch, said at least one of the series-connected circuits being further connected with said envelope-forming capacitor in parallel, and said time-constant change switch being so arranged that said current-limiting element is thereby short-circuited or not short-circuited.

The nature, principle, details, and utility of the invention will be more clearly apparent from the following detailed description with respect to preferred embodiments thereof, when read in conjunction with the accompanying drawings, in which like parts are designated by like reference numerals and characters. a

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 2 illustrates an improved switching circuit constituting an embodiment of the present invention;

FIG. 3a, 3b) are waveform diagrams showing the output signals and their envelopes obtained from the switching circuit of FIG. 2 at its different operational conditi'on'si I FIG. 4 illustrates a switching circuit constituting another embodiment of the present invention;

FIG. 5 is a voltage diagram showing the variation of voltage at point [2 in the switching circuit of FIG. 4; and

FIG. 6 is a circuit diagram of a switching circuit which constitutes still another embodiment of I this invention, and whereby a multitude of different values of the time constant may be selected.

DETAILED DESCRIPTION The switching circuit according to the present invention will now be described with reference to FIG. ZLTWhen the emitter potential, i.e.. the potential at a point a in this drawing becomes lower than the base potential'of a transistor TR, an input signal of the transistor TR can pass through the transistor, andian output signal isobtained from the output terminals. The transistor is used as a gate.

At the terminals 1 and 2, potentials -E, nd -E are respectively applied (|E IE Accordingly, if key switches K, and K Ja re placed at the indicated positions, a capacitor C, is charged with the difference voltage (--E,) (E,,, and another capacitor C is also charged with this voltage difference because a diode connected in "series with the capacitor C,-is in the forward bias.

If, with the circuit in this state, the key switch K, is closed, the electric charge in the capacitor C is discharged through a resistor R,. As a result, the potential at the point a, thatis, the emitter potential of the transistor TR will be lowered to a value substantially equal -E maintaining a time constant of 1 C ,R,, and a signal having a rising configuration of envelope in accordance with the above described variation of the emitter potential will appear at the collector side of the transistor TR. Since a resistor to provide a bias potential for the base of the transistor TR is so selected that, when'the key switch K, is closed, the emitter potential is always lower than the base potential, the input signal is continuously passed through the transistor TR and appears at the collector side thereof. During this time, however, the capacitor C cannot be discharged through the resistor R, because of existence of a reversely biased diode D. This means that, even if the key switch K, is closed, the influence of C 'will not affect the shape of the envelope and the shape is varied with a time constant of r C,R,.

If the key-switch K, is opened again, the capacitor C, which has been discharged, when the key-switch K, is closed, is now charged again through the'resistor R with the potential source of (-E,) (E,), and the potential at the point a, i.e. the emitter potential of the transistor TR, is varied from E, to

-E, corresponding to the time constant 1' z C,R,, whereby the base potential of the transistor TR is brought back into the region lower than the emitter potential. As a result, the input signal can no longer pass through the transistor TR to the collector side. Because the capacitor C has not been discharged at the time the key-switch K, is closed, due to the reverse bias potential caused by the diode D, no charging of C, will occur when the key-switch K, is opened again, and no influence of C will appear in the attenuation process of the envelope.

More specifically, when the time constant change switch K is opened, even if the key-switch K, is open or closed, the capacitor C will have no influence on the time-constants for determining the configuration of the envelope of the output signal, and the time-constants will be approximately equal to C,R, for the rising portion of the envelope and toC,R for the attenuation portion thereof.

When the time-constant change switch K, is closed, the diode D is short-circuited by the switch K and the capacitors C, and C are connected in parallel. Consequently, the time constants at the time the signal is switched on-and-off may be varied by the sum of the capacitances of capacitors (C, C and the output signal appears at the collector side of the transistor will be varied in accordance with the time constant 1 (C, C )R, when the key switch K, is closed, and with the time constant 1 (C, C )R when the key switch K, is opened.

Accordingly, the values of the time constants when the keyswitch K, is open and closed at the time the time-constant change switch K is closed may be larger than those time constants at the time the time-constant transfer switch K is left opened. In this embodiment of the invention since the values of the capacitor C is so determined that: C (l- 20)C,, the time constants for determining the shape of the envelope may be increased by from to times those in the case where the switch K, s opened. FIGS. 3a, 3b illustrate the configurations of the signals in both of the above described cases, wherein FIG. 3a shows the waveform of the signal at the time the key-switch K, is closed and opened with the time constant change switch K maintained in the opened state, and FIG. 312 indicates the same at the time the key-switch K, is closed and opened with the time constant change switch K maintained in the closed state. Ordinarily, the switch K, is actuated by the respective key in the keyboard, and the switch K is actuated by a tablet or lever specifically provided for changing the envelope configuration.

Although, the embodiment of the invention shown in FIG. 2. has been described as having a diode D connected in series with the capacitor C a resistor R, as indicated in FIG. 4 may also be employed instead of the diode D. In such a case, the value of the resistor R is so selected that following conditions are satisfied: R R,, R R C 11 0.1 to 0.5 sec. When such a selection is made, the operation of the switching circuit of FIG. 4, at the time the time constant change switch K is closed, is substantially similar to that of the example shown in FIG. 2, and a larger value of the capacitance (C, C is thereby obtained.

When the time constant transfer switch K is left opened and if the key-switch K, is at first closed and then opened, the potential at a point b of FIG. 4 is varied as indicated in FIG. 5, the potential variation being mainly determined by the variation of the capacitance C,. If the base potential of the transistor TR is determined to a level indicated in FIG. 5, an envelope corresponding to a smaller time constant may be obtained as described with reference to FIG. 2. Although, in the circuits illustrated in FIGS. 2 and 4, the diode D or resistor connected in series with the capacitor C might be omitted altogether, such an arrangement would cause an undesirable feature wherein the capacitor C is not charged when the keyswitch K, is opened, and this might cause an unwanted signal delivered at the moment when the switch K is closed as preparation for slow rising and decaying.

FIG. 6 indicates still another embodiment of the present invention in which a plurality of series connected circuits, each consisting of a capacitor and a diode, are connected in parailel with the capacitor C,, and the junction points between the capacitors and the diodes are connected respectively to the corresponding fixed contacts of the time constant changing switch K Each of the capacitors C, to C, may be determined,

for instance, 9! g 2 and so on, or 2 2 :23; 1 10 100 and so on. In this arrangement, if the key-switch K, is first closed and then opened, with any one K of the time constant change switches being closed, an envelope corresponding to a desired time constant can be obtained.

Since the construction and organization of the switching circuit in accordance with the present invention is as described above, crisp sounds well adapted to jazz music and the like, having switched time envelopes corresponding to smaller time constants, can be obtained with the switch K kept in an opened state. On the other hand, with the switch K kept in the closed position, smooth sounds well adapted to the mood music having envelopes corresponding to larger time constants can be obtained. I

Accordingly, with one musical instrument, two kinds of sounds can be selectably obtained, such a feature constituting an advantageous effect of the present invention.

Furthermore, since a diode or a resistor is connected in series with the capacitor C,,, the capacitor is always charged even though the key switch K, is not depressed, and the possibility of unwillful sending out of a signal, at the moment the time constant change switch is closed, is completely eliminated.

I claim:

1. A switching circuit to be used in an electronic musical instrument comprising: a gate, a first capacitor whose charge controls an envelope of said gate, a key switch connected parallel to the first capacitor, at least one of series-connected circuits each consisting of a further capacitor and a currentlimiting element, and a time-constant change switch, said at least one of the series-connected circuits. being further con:- nected with said first capacitor in parallel, and said time-con stant transfer switch being so arranged that said current-limiting element is thereby short-circuited or not short-circuited.

2. A switching circuit to be used in an electronic musical instrument as defined in claim 1 wherein said current-limiting element is a diode conducting when the key switch is in off state. I

3. A switching circuit to be used in an electronic musical instrument as defined in claim 1 wherein said current-limiting element is a resistor.

4. A switching circuit to be used in an electronic musical in strument as defined in claim 1 wherein a plurality of said se ries-connected circuits each consisting of a capacitor of large; capacitance and a diode is further connected in parallel w u said envelopeforming capacitor, and 'said time-constant change switch includes a plurality of positions correspondin the number of said series-connected circuits. 

1. A switching circuit to be used in an electronic musical instrument comprising: a gate, a first capacitor whose charge controls an envelope of said gate, a key switch connected in parallel to the first capacitor, at least one of series-connected circuits each consisting of a further capacitor and a currentlimiting element, and a time-constant change switch, said at least one of the series-connected circuits being further connected with said first capacitor in parallel, and said timeconstant transfer switch being so arranged that said currentlimiting element is thereby short-circuited or not shortcircuited.
 2. A switching circuit to be used in an electronic musical instrument as defined in claim 1 wherein said current-limiting element is a diode conducting when the key switch is in off state.
 3. A switching circuit to be used in an electronic musical instrument as defined in claim 1 wherein said current-limiting element is a resistor.
 4. A switching circuit to be used in an electronic musical instrument as defined in claim 1 wherein a plurality of said series-connected circuits eacH consisting of a capacitor of larger capacitance and a diode is further connected in parallel with said envelope-forming capacitor, and said time-constant change switch includes a plurality of positions corresponding the number of said series-connected circuits. 